What is the structural and functional unit of the kidney?

In a rabbit,the urinary bladder opens into:

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Nephrons are of two types: Cortical and Juxta-medullary,based on their relative position in the cortex and medulla.
Reason $R$: Juxta-medullary nephrons have a short loop of Henle,whereas cortical nephrons have a longer loop of Henle.
In the light of the above statements,choose the correct answer from the options given below:

Distinguish between: Juxtamedullary and Cortical nephrons.

Identify the odd one out.

Write a short note on the types of nephrons.